| Vestibulocochlear nerve | |
|---|---|
 The course and connections of thefacial nerve in thetemporal bone | |
 Inferior view of the human brain, with the cranial nerves labelled. | |
| Details | |
| To | Cochlear nerve,vestibular nerve |
| Innervates | Hearing,balance |
| Identifiers | |
| Latin | nervus vestibulocochlearis |
| MeSH | D000159 |
| NeuroNames | 553 |
| TA98 | A14.2.01.121 |
| TA2 | 6307 |
| FMA | 50869 |
| Anatomical terms of neuroanatomy | |
| Cranial nerves |
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Thevestibulocochlear nerve orauditory vestibular nerve, also known as theeighth cranial nerve,cranial nerve VIII, or simplyCN VIII, is acranial nerve that transmitssound andequilibrium (balance) information from theinner ear to thebrain. Througholivocochlear fibers, it also transmits motor and modulatory information from thesuperior olivary complex in the brainstem to thecochlea.[1]
The vestibulocochlear nerve consists mostly ofbipolar neurons and splits into two large divisions: thecochlear nerve and thevestibular nerve.
Cranial nerve 8, the vestibulocochlear nerve, goes to the middle portion of thebrainstem called thepons (which then is largely composed of fibers going to thecerebellum). The 8th cranial nerve runs between the base of the pons andmedulla oblongata (the lower portion of the brainstem). This junction between the pons, medulla, and cerebellum that contains the 8th nerve is called thecerebellopontine angle.The vestibulocochlear nerve is accompanied by thelabyrinthine artery, which usually branches off from theanterior inferior cerebellar artery at the cerebellopontine angle, and then goes with the 7th nerve through theinternal acoustic meatus to the internal ear.
The cochlear nerve travels away from thecochlea of theinner ear where it starts as thespiral ganglia. Processes from theorgan of Corti conduct afferent transmission to the spiral ganglia. It is theinner hair cells of the organ of Corti that are responsible for activation of afferent receptors in response to pressure waves reaching thebasilar membrane through the transduction of sound. The exact mechanism by which sound is transmitted by theneurons of the cochlear nerve is uncertain; the two competing theories areplace theory andtemporal theory.
The vestibular nerve travels from thevestibular system of the inner ear. Thevestibular ganglion houses the cell bodies of thebipolar neurons and extends processes to five sensory organs. Three of these are thecristae located in the ampullae of thesemicircular canals. Hair cells of the cristae activate afferent receptors in response to rotational acceleration. The other two sensory organs supplied by the vestibular neurons are the maculae of thesaccule andutricle. Hair cells of the maculae in the utricle activate afferent receptors in response to linear acceleration, while hair cells of the maculae in the saccule respond to vertically directed linear force.
The vestibulocochlear nerve is derived from theembryonicotic placode.
This is thenerve along which the sensory cells (the hair cells) of the inner ear transmit information to thebrain. It consists of the cochlear nerve, carrying details abouthearing, and the vestibular nerve, carrying information aboutbalance and spatial orientation.It emerges from thepontomedullary junction and exits the innerskull via the internal acoustic meatus in thetemporal bone.
The vestibulocochlear nerve carries axons of typespecial somatic afferent.
Damage to the vestibulocochlear nerve may cause the following symptoms:
Examinations that can be done include theRinne andWeber tests.
Rinne's test involves Rinne's Right and Left Test, since auditory acuity is equal in both ears. Ifbone conduction (BC) is more than air conduction (AC) (BC>AC) indicates Rinne Test is negative or abnormal. If AC>BC Rinne test is normal or positive. If BC>AC and Weber's test lateralizes to abnormal side then it is Conductive hearing loss. If AC>BC and Weber's test lateralizes to normal side then it concludes Sensorineural hearing loss.
After pure-tone testing, if the AC and BC responses at all frequencies 500–8000 Hz are better than 25 dB HL, meaning 0-24 dB HL, the results are considered normal hearing sensitivity. If the AC and BC are worse than 25 dB HL at any one or more frequency between 500 and 8000 Hz, meaning 25+, and there is a no bigger difference between AC and BC beyond 10 dB at any frequency, there is a sensori-neural hearing loss present. If the BC responses are normal, 0-24 dB HL, and the AC are worse than 25 dB HL, as well as a 10 dB gap between the air and bone responses, a conductive hearing loss is present.{updated March 2019}
The modified Hughson–Westlake method is used by many audiologists during testing. A battery of (1) otoscopy, to view the ear canal and tympanic membrane, (2) tympanometry, to assess theimmittance of the tympanic membrane and how well it moves, (3) otoacoustic emissions, to measure the response of the outer hair cells located in the cochlea, (4) audiobooth pure-tone testing, to obtain thresholds to determine the type, severity, and pathology of the hearing loss present, and (5) speech tests, to measure the patients recognition and ability to repeat the speech heard, is all taken into consideration when diagnosing the pathology of the patient.
Some older texts call the nerve theacoustic orauditory nerve,[3] but these terms have fallen out of widespread use because they fail to recognize the nerve's role in the vestibular system.Vestibulocochlear nerve is therefore preferred by most.
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